Gerhard, you have made an important point. It is possible that the 220uf cap on the current source could throw things off. I think that a J203 fet could replace the 1K resistor. It is true that 2ma is a bit low, but with too much current would give too high a Vp and make for a higher voltage initial supply. It seems to me that the shunt fet is really an open loop follower, so the output impedance of the regulator is really 1/gm of the fet itself. The 220uf cap in that circuit is probably OK.

very interesting post of yours.
So the classic LM317 is not that bad.
Could you give me some hints about the topology you use with it?
I am very interested in +/- 30V dual supply.
Thank you so much.
And of course my sincere congratulations for your excellent creations !

Originally posted by poobah I only ask because in both circuits your Vout is very dependant on the Vgsth & the gm of the FET.

The Tl431 is not controlling the output voltage but rather the gate... I realize this may be exactly your intent. But this circuit will not have the lowest output impedance as compared to other topologies.

Are you trying to avoid the TL431 from exerting direct control over the output voltage in an effort to reduce noise?

Poobah, My intent is to simultaneously have a low noise (RC filter after the TL431) and an open loop configuration, as I can get a quite low output impedance (2 Ohm or less) without feedback. I prefer this than the drawbacks of a feedback shunt regulation.

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Originally posted by gerhard I think that in both figs the role of the 220u cap has not been engineered in but comes from gut feeling. "We'll decouple everyting to GND, that can't be bad." But in Fig.1 we open the doors to ripple & noise, and in Fig. 2 we spoil the high impedance of the current source.

Gerhard, you are absolutly right about the 220uF capacitor (ground to base in both figures).
Yes it ¡¥s more by practice... however concerning the fig2, I still need to think of it more in depth, the zener noise is shunted on the base side by the 220uF capacitor and on the other side (emitter-resistor) shunted to ground by the mosfet¡K and this is why I said that I preferred the fig2 circuit.

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Originally posted by john curl Gerhard, you have made an important point. It is possible that the 220uf cap on the current source could throw things off. I think that a J203 fet could replace the 1K resistor. It is true that 2ma is a bit low, but with too much current would give too high a Vp and make for a higher voltage initial supply. It seems to me that the shunt fet is really an open loop follower, so the output impedance of the regulator is really 1/gm of the fet itself. The 220uf cap in that circuit is probably OK.

Yes John it's possible that this capacitor "throw things off", as I said to Gerhard, but for fig2 circuit, I have to think of it some more, in any case as soon as I would have more time I would make measurements on a real circuit, starting with my "old" test circuit.
Yes of course the 1k resistor must be replaced by a fet, the 2 mA value was more to use for leds but I have no led spice models to represent them, of course 5mA is best suited for zeners.
For the moment these circuits are rather intended to study the "direction" of the BJT current source related to the preregulator and the shunt device.

”…However, with the 10 ohm resistor you have dropped your potential noise contribution by the current source about 10/.125 or about 80 times.That 10 ohm resistor pads the transconductance of the transistor that much! Perhaps, you knew that, Richard, but I hope that I can point this out to others, who might be looking at these circuits.¨

About the preceding post, I suppose you speak about Gm=1/Re and Re=26/Ic, I knew this, so to optimize the noise contribution of the current source, John could you give us some noise values for say 2.2V, 4.7V and 15v zeners as well as for led's please or even some hints on noise/impedance vs. current for these devices (I have read the Vishay datasheet on zeners but there is nothing on noise, and either for leds, where the impedance is not stated (I measured it and according to the colours and current, values goes from 40 to 80 Ohms, 1mA < If < 5mA).

Richard, another factor is the beta of the C45 transistor. I have been working with fets for so long, that I forgot to put that in, however it would seem that you need at least 2 ma to bias the transistor to its operating current. That would leave no current for the zener! It would seem that you need a low current j113 fet, let's say 10ma or so for a bias fet. I doubt that you could get away with 1K, in any case. Am I missing something else, Gerhard?

All this discussion begin cast up " science for science ".... Can John Curl, as most experienced of us, to tell, which aspect of sound will be changed by using similar regulator in oposite to " normal one " ? I like complicated circuits, but all must have sense....

Well said ! I am in a full agreement with you., Upupa... . (Rare, eh ? LOL !).

Some guys have little more answers to our questions (than others claim to...). Hence your valuable question... They are not really gurus... Are they ? But they are much more experienced as we are, as amateurs...

And here lies the problem : on the forum full beginners are crossing end of professional life engineers, soldering technicians cross full chief engineers, digital world crosses analog. world, and so on... Where is the problem ?

It is around serious and possible terms... 60 years old guys claiming that they can still hear 16 Khz at 0 dB are still astonishing per my data (ever with the Loudness button pushed on !!!). Or both !!!! Eh, Elso ?... (Both Fletcher & Munson and Baxendall would be wrong at the same time)... But LOL !

No chance that those people really wnat to exchange data here... They are just NOT in their own universe... And far too prone to shout one out.. Only PRIVATE messages around make the forum go seemingly round...

That's why I am slowly but consistently ripping off this forum... And it is just my 2 cents...

But, anyway, thanks for valuable inputs (as it made my time taking English lessons not fully unuseful !).

Richard, what I am most concerned with is the 1K resistor. Looking more carefully at your complete schematic, I see that you have only a 2V differential across the 1K resistor and this implies that all the current from the resistor goes into the transistor to supply the base current. Is the 3V device even turned on? Anyway, why not put the 1K resistor to ground. Wouldn't that work OK?
As far as design philosophy is concerned, I like to think about new ways of making circuits. Sometimes, I see a new way of looking at a circuit on this website. I find that interesting. However, why don't I like normal IC regulators that much? Well, they are noisy, have bad transient response, and fall apart at high frequencies. I prefer, myself, to use an active IC regulator in series with a simple high speed fet cap follower. This gives me the DC stability of the feedback regulator with the high speed response and low noise of the fet follower. That is my approach. I know that some circuits may be less critical of power supply effects, but I do know that complementary cascode circuits are VERY sensitive to power supplies. That I why I put so much effort into power supplies.